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Biomedical subjects

Thomas J Palmeri

Publications and source records attributed to Thomas J Palmeri.

8 recordsLinked to original sources
PubMed2006

Perceptual interaction between real and synesthetic colors.

People with color-graphemic synesthesia experience vivid, reliable color upon viewing achromatic alphanumeric characters. Recent evidence indicates that synesthetic color experiences are as perceptually real as actual colors are for non-synesthetic observers. To investigate possible interactions between real and synesthetic colors, we tested two adult color-graphemic synesthetes on a pair of perceptual grouping tasks. In Experiment 1, we employed a well-known phenomenon of motion perception, bistable apparent motion, to explore whether synesthetic colors interact with real colors in grouping over time. Two-frame apparent motion sequences were presented with both path lengths and colors systematically manipulated. Results showed that synesthetic colors of motion tokens interacted with matching real colors of the corresponding motion tokens, which could subsequently bias perceived direction of motion. In Experiment 2, we exploited binocular rivalry, a condition under which two dissimilar monocular images compete with each other and result in perceptual switches, to explore whether synesthetic colors interact with real colors in grouping over space. Pairs of rival images with two different characters were presented dichoptically with colors of characters manipulated. Results showed that synesthetic and real colors of characters tended to group together, which, in turn, promoted the perceived global dominance during binocular rivalry. Therefore, the present results identify substantial interaction between synesthetic colors and real colors in perceptual grouping.

Adult↗
PubMed2006

Theory-based categorization under speeded conditions.

It is widely accepted that similarity influences rapid categorization, whereas theories can influence only more leisurely category judgments. In contrast, we argue that it is not the type of knowledge used that determines categorization speed, but rather the complexity of the categorization processes. In two experiments, participants learned four categories of items, each consisting of three causally related features. Participants gave more weight to cause features than to effect features, even under speeded response conditions. Furthermore, the time required to make judgments was equivalent, regardless of whether participants were using causal knowledge or base-rate information. We argue that both causal knowledge and base-rate information, once precompiled during learning, can be used at roughly the same speeds during categorization, thus demonstrating an important parallel between these two types of knowledge.

Association Learning↗
PubMed2004

Computational approaches to the development of perceptual expertise.

Dog experts, ornithologists, radiologists and other specialists are noted for their remarkable abilities at categorizing, identifying and recognizing objects within their domain of expertise. A complete understanding of the development of perceptual expertise requires a combination of thorough empirical research and carefully articulated computational theories that formalize specific hypotheses about the acquisition of expertise. A comprehensive computational theory of the development of perceptual expertise remains elusive, but we can look to existing computational models from the object-recognition, perceptual-categorization, automaticity and related literatures for possible starting points. Arguably, hypotheses about the development of perceptual expertise should first be explored within the context of existing computational models of visual object understanding before considering the creation of highly modularized adaptations for particular domains of perceptual expertise.

Attention↗
PubMed2002

The perceptual reality of synesthetic colors.

Synesthesia is a remarkable, rare condition where an individual has multimodal perceptual experiences from a unimodal sensory event. We have studied such an individual, an adult male for whom achromatic words and alphanumeric characters are seen in vivid, reliable colors. We used a variety of perceptual tasks to document the perceptual reality of synesthetic colors and to begin to localize the stage of visual processing where this anomalous binding of externally specified form and internally generated color may take place. Synesthetic colors were elicited by forms defined solely by binocular cues or solely by motion cues, which implies a central locus of visual processing for synesthetic binding of form and color. Also included among our measurements was a difficult visual search task on which non-synesthetic subjects required an effortful search through the visual display. Our subject, in contrast to non-synesthetic subjects, accomplished the task with relative ease because the target of the search had a different synesthetic color from the distractors. Thus, synesthetic experiences appear to originate from a binding of color and form that takes place within central stages of visual processing.

Adult↗
PubMed2002

Are there representational shifts during category learning?

Early theories of categorization assumed that either rules, or prototypes, or exemplars were exclusively used to mentally represent categories of objects. More recently, hybrid theories of categorization have been proposed that variously combine these different forms of category representation. Our research addressed the question of whether there are representational shifts during category learning. We report a series of experiments that tracked how individual subjects generalized their acquired category knowledge to classifying new critical transfer items as a function of learning. Individual differences were observed in the generalization patterns exhibited by subjects, and those generalizations changed systematically with experience. Early in learning, subjects generalized on the basis of single diagnostic dimensions, consistent with the use of simple categorization rules. Later in learning, subjects generalized in a manner consistent with the use of similarity-based exemplar retrieval, attending to multiple stimulus dimensions. Theoretical modeling was used to formally corroborate these empirical observations by comparing fits of rule, prototype, and exemplar models to the observed categorization data. Although we provide strong evidence for shifts in the kind of information used to classify objects as a function of categorization experience, interpreting these results in terms of shifts in representational systems underlying perceptual categorization is a far thornier issue. We provide a discussion of the challenges of making claims about category representation, making reference to a wide body of literature suggesting different kinds of representational systems in perceptual categorization and related domains of human cognition.

Analysis of Variance↗
PubMed2002

Modeling individual differences in perceptual and attentional processes related to bulimic symptoms.

Attentional and perceptual differences between women with high and low levels of bulimic symptoms were studied with techniques adapted from cognitive science. Stimuli were pictures of young women varying in body size and facial affect. A multidimensional scaling analysis showed that the high-symptom women were significantly more attentive to information about body size and significantly less attentive to information about affect. In prototype classification tasks, the high-symptom women used significantly more information about body size and significantly less information about affect. There were strong associations between individual differences in attention in the similarity task and decision making in the classification tasks. The study shows the potential utility of cognitive science methods for the study of cognitive factors in psychopathology.

Adult↗